When the rapid aging of populations is becoming a clear trend all over the world, the impairment of mobility is becoming an increasingly challenging problem affecting a large number of individuals. People’s physical mobility may decrease due to a variety of causes, including age-related decline of physical work capacity, neuromuscular diseases, and injuries (such as spinal cord injury, SCI). With impaired mobility, people tend to be less physically active and more likely to suffer from various health conditions (obesity, depression, high blood pressure, etc.). The shortage of caregivers further exacerbates the problem.
Our research aims at addressing these challenges with an integrated assistive system that incorporates a variety of robots with different yet complementary functions, including wearable and semi-wearable robots, wheeled and legged robotic platforms, and rail-sliding assistive robots. Specifically on the wearable/semi-wearable robots, our research is focused on a portable power-assist ankle-foot orthosis to improve gait quality, and a novel semi-wearable device for sit-to-stand assistance.
Portable Ankle-Foot Orthosis
The ankle plays an important energetic role in human locomotion. In the level walking of healthy adults, the ankle processes substantially more work than the knee and hip. However, the lack of ankle push-off power forces older adults to adopt a different strategy in walking, placing heavier loads in the knee and hip joints. The powered ankle-foot orthosis in our research is developed to address this problem by supplementing the push-off power in the ankle to obtain a more natural gait, and improve the user’s muscle performance through a novel assistive-resistive training strategy.
To obtain a powerful yet lightweight device, the orthosis actuator is constructed with a high-torque-output flat motor combined with a two-stage compact transmission. A multi-dof joint design minimizes the device’s constraint to the joint’s natural movement without sacrificing the reliable torque output for foot plantar- and dorsi-flexion. We are also investigating a new serial-elastic-actuator (SEA) concept, which incorporates a carbon-fiber flat spring-based elastic element to replace the traditional coil spring to achieve significant weight reduction while maintaining the advantages of the traditional SEA design (reduced shock loading, mechanical energy storage, integrated torque sensing, etc.). Combining the novel actuator design with the innovations in orthosis control and gait training strategy, we hope to develop a portable orthosis system practical for people’s daily use, serving as a long-term solution to the mobility impairment problem.
Semi-Wearable Sit-to-Stand Assist (SW-SiStA)
The purpose of SW-SiStA is to help a frail user to stand up from a seated position more easily. Existing sit-to-stand devices are heavy, bulky, and difficult to maneuver, who diminishes their usefulness in the home environment.
Our early research attempted to address this problem with a powered knee orthosis, which provides direct assistance to the user’s knee motion through its joint actuator. The resulted orthosis prototype was able to provide effective assistance, but it also suffers from the issue of added burden to the user in walking. Subsequently, the knee orthosis evolved into a portable assistive device, which can be easily detached from the user after standing up. As such, the user can enjoy the powered assistance during standing-up while avoiding the added burden in walking.
The current prototype of the SW-SiStA is powered with a pneumatic cylinder-type actuator, which is especially suitable for the intended application. In the standing up process, the knee joint generates a very high torque to initiate the upward motion, and the torque gradually decreases with the standing-up process and eventually reduces to nearly zero. Corresponding to this process, the pneumatic actuator in the assistive device generates a large assistive force when pressurized with compressed air, in order to help the user to initiate the upward motion. Subsequently, the actuator chamber is closed to avoid further energy consumption, and the actuator force naturally reduces when the chamber volume expands and air pressure drops during the standing-up process. As a result, the energy consumption is significantly reduced by leveraging such air pressure dynamics. Furthermore, the energy consumption can be further reduced when the sitting down process is taken into consideration, as the air in the actuator chamber is compressed in the sitting-down process, and the compressed air can be stored and reused for the stand-up assistance in the next cycle.